CA2186935C

CA2186935C - Biaxially oriented polyester film to be formed into containers

Info

Publication number: CA2186935C
Application number: CA 2186935
Authority: CA
Inventors: Masahiro Kimura; Kohzo Takahashi; Koichi Abe
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 1995-10-02
Filing date: 1996-10-01
Publication date: 2005-01-04
Anticipated expiration: 2016-10-01
Also published as: DE69628522D1; MY115854A; KR970070060A; US6610378B1; KR100462168B1; EP0767049B1; CN1158781A; EP0767049A2; EP0767049A3; CA2186935A1; CN1134334C; DE69628522T2

Abstract

A biaxially oriented polyester film to be formed into containers, comprising a polyester containing 93 mol% or more of ethlyene terephtlalate as a component, and the breaking elongation in the machine direction (S MD) and the breaking elongation in the transverse direction (S TD), satisfying [Formula 1] and [Formula 2], or a biaxially oriented polyester film to be formed into containers, comprising a polyester containing 93 mol% or more of ethylene terephthalate as a component, and the face orientation coefficient, being 0.01 to less than 0.13, or a biaxially oriented polyester film to be formed into containers, comprising a polyester containing 95 mold or more of ethylene terephthalate as a component, and the amorphous Young's modulus, being 120 to 220 kg/mm2, is respectively suitable for containers, especially as a film on the inner and outer faces of metallic cans, since it is excellent not only in formability but also in impact resistance and taste property.
[Formula 1]
140% <=(s MD + S TD) /2 <= 300%
S MD: Breaking elongation in the machine direction S TD: Breaking elongation in the transverse direction [Formula 2]
¦S MD - S TD¦ <= 60%

Description

SPECIFICATION
A biaxially oriented polyester film to be formed into containers Technical field The present invention relates to a polyester film to be formed into containers, excellent not only in formability but also in impact resistance and taste property. In more detail, it relates to a biaxially oriented polyester film to be suitably formed together with a metallic sheet into metallic cans.
Background art Containers such as metallic cans are produced by forming, for example, by drawing and ironing a polyester film alone, or after laminating it on a substrate made of a metal or non-metallic material.(paper, plastic material, fibrous material, or nonwoven fabric, etc.), etc.
Above all, the thermal lamination of a film on a metallic sheet attracts attention, as the production of metallic cans grows recently.
It had been widely practiced, for the purpose of preventing corrosion, to internally coat the metallic can with a solution or dispersion of any of various epoxy-based or phenol-based thermosetting resins dissolved or dispersed in any solvent, for covering the internal surface of the metal. However, such a method of covering with a thermosetting resin takes a long ~ 186935 ~.. _ time for drying the coating material, to lower the productivity, and requires the use of an organic solvent in a large amount unpreferably in view of environmental pollution.
To solve these problems, it is proposed to laminate a polyester film on a steel sheet or aluminum sheet destined to be metallic cans, or on any of these metallic sheets treated on the surface by any of various methods such as plating, and then to draw and iron the film-laminated metallic sheet for production of metallic cans. In this case, the polyester film is required to have the following properties:
(1) The polyester film should be excellent in formability, without causing such defects as pinholes after completion of forming.

(2) The polyester film should not be peeled, cracked or pinholed when any impact acts on the metallic can.

(3) The polyester film should not adsorb the flavor component of the content of the metallic can or should not get any of its components dissolved to impair the flavor of the content of the metallic can.
Many proposals have been made to meet these requirements. For example, Japanese Patent Laid-Open (Kokai) No. 2-305827 discloses a polyester film with a specific face orientation coefficient; Japanese Patent Laid-Open (Kokai) No. 2-57339, a copolymerized polyester film with specific crystallinity; and Japanese Patent Laid-Open (Kokai) No. 3-93525, a film made less oriented and less dense mainly by blending with a copolymer. However, these proposals cannot satisfy all the above mentioned requirements, and cannot be said to be satisfactory especially in the compatibility between formability and impact resistance, or in taste property.
Furthermore, containers obtained by laminating an olefin based polymer and a metal or paper, etc. are remarkably poor in taste property disadvantageously.
Disclosure of the invention The object of the present invention is to solve the above mentioned problems of prior arts, and to provide a biaxially oriented polyester film to be formed into containers, excellent in formability, impact resistance and taste property, particularly to provide a biaxially oriented polyester film to be suitably formed together with a metallic sheet into metallic cans.
The object of the present invention can be achieved by a biaxially oriented polyester film to be formed into containers, comprising a polyester containing 93 mold or more of ethylene terephthalate as a component, and the breaking elongation in the machine direction (S MD) and the breaking elongation in the transverse direction (S TD), satisfying [Formula 1] and [Formula 2], or a biaxially oriented polyester _ ~,,..:
film to be formed into containers, comprising a polyester containing 93 mold or more of ethylene terephthalate as a component, and the face orientation coefficient, being 0.01 to less than 0.13, or a biaxially oriented polyester film to be formed into containers, comprising a polyester containing 95 mold or more of ethylene terephthalate as a component, and the amorphous Young's modulus, being 120 to 220 kg/mm2.
[Formula 1]
140 s (S MD + S TD)/2 s 300 S MD: Breaking elongation in the machine direction S TD: Breaking elongation in the trarwerse direction [Formula 2]
~S MD - S TDI 5 6 Most preferred embodiments The polyester in the present invention is a polyester containing 93 mold of ethylene terephthalate as a component, in view of the incapability of adsorbing the flavor component of the content of the container and good heat resistance. The polyester can contain another component copolymerized as far as the intended properties are not impaired. The dicarboxylic acid for the other component can be selected, for example, from aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenoxyethanedicarboxylic acid, 5-sodiumsulfoisophthalic acid, and phthalic acid, aliphatic dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, dimer acid, malefic acid, and fumaric acid, alicyclic dicarboxylic acids such as cyclohexynedicarboxylic acid, hydroxycarboxylic acids such as p-hydroxybenzoic acid. On the other hand, the glycol for the other component can be selected, for example, from aliphatic glycols such as propanediol, butanediol, pentanediol, hexanediol, and neopentyl glycol, alicyclic glycols such as cyclohexanedimethanol, aromatic glycols such as bisphenol A, and bisphenol S, diethylene glycol, polyalkylene glycol, etc.
Respectively two more of the above dicarboxylic acids and glycols can also be used together.
Moreover, as far as the object of the present invention is not impaired, the polyester of the present invention can be copolymerized with a polyfunctional compound such as trimellitic acid, trimesic acid, or trimethylolpropane, etc.
In the present invention, especially for applications severe in taste property, the ethylene terephthalate content is preferably 95 mold or more, more preferably 97 mold or more.
Furthermore, in the present invention, in view of better impact resistance and taste property, the intrinsic viscosity is preferably 0.5 to 1.5, and especially in view of higher impact resistance, it is preferably 0.7 to 1.5, more preferably 0.81 to 1.5, further more preferably 0.83 to 1.5.
A larger intrinsic viscosity is considered to increase the chance that molecules are more intertwined, and as a result, to improve impact resistance and to minimize the flavor component adsorbability.
The intrinsic viscosity [r~] can be obtained by dissolving the polymer into o-chlorophenol, and measuring the relative viscosity at 25°C.
Moreover, in view of better taste property, the acetaldehyde content of the polyester film is preferably 30 ppm or less, more preferably 25 ppm or less, further more preferably 20 ppm or less. An acetaldehyde content of more than 30 ppm may deteriorate the taste property. The method for keeping the acetaldehyde content of the film at 30 ppm or less is not especially limited. For example, the polyester can be annealed under reduced pressure or in an inactive gas atmosphere at a temperature lower than the melting point of the polyester, to remove the acetaldehyde produced by the thermal decomposition during the production of the polyester by polycondensation reaction, etc. As another method, the polyester can be polymerized in a solid phase preferably under reduced pressure or in an inactive gas atmosphere at a temperature higher than 150°C and lower than the melting point.
As a further other method, the polyester can be melt-formed ry ~
into a film using a vent type extruder. As a still further other method, the polyester can be melt-extruded at a temperature of melting point + 30°C or less, preferably melting point + 20°C or less, more preferably melting point + 15°C or less in a short time. These methods are effective also for obtaining a film high in intrinsic viscosity.
To obtain a film high in intrinsic viscosity, it is preferable to keep the water content of the polyester chips at 100 ppm or less, preferably 50 ppm or less, further more preferably 30 ppm or less.
Furthermore, in view of taste property, the polyester film of the present invention contains preferably 1 to 500 ppm, more preferably 5 to 300 ppm, further more preferably 10 to 100 ppm of germanium. If the germanium content is too low, the effect for improving the taste property may be insufficient, and if too large, foreign matters may be generated in the polyester to lower the impact resistance and to deteriorate the taste property. The polyester of the present invention can be improved in taste property by containing said specific amount of germanium. The method for letting the polyester contain germanium is not especially limited, but it is preferable to add a germanium compound as a polymerization catalyst at any optional step before the production of the polyester is completed. For example, a germanium compound can be added as a powder. As another method, as described in Japanese Patent Publication (Kokoku) No. 54-22234, a germanium compound can be dissolved into the glycol used as a starting raw material of the polyester. The germanium compound can be selected, for example, from germanium dioxide, germanium hydroxide containing crystal water, germanium alkoxide compounds such as germanium tetramethoxide, germanium tetraethoxide, germanium tetrabutoxide, and germanium ethyleneglycoxide, germanium phenoxide compounds such as germanium phenolate and germanium (3-naphtholate, phosphorus-containing germanium compounds such as germanium phosphate and germanium phosphite, germanium acetate, etc. Among them, germanium dioxide is preferable.
Furthermore, the amount of the carboxyl terminal groups of the polyester film of the present invention is preferably 40 equivalents/ton or less in view of impact resistance and taste property. Especially when the amount of the carboxyl terminal groups is 35 equivalents/ton or less, the recoverability and impact resistance of the film are better preferably.
Specifically, it is preferable to decrease the carboxyl terminal groups of the raw polyester by ~ Solid phase polymerization ~ using a known terminal blocking agent such as carbodiimide or oxazoline to a predetermined amount, and ~
extruding at a low temperature in a short time.
On the other hand, increasing the amount of carboxyl terminal 218b93~
groups in the surface by surface treatment, etc. is preferable for improving the adhesive strength.
The polyester film of the present invention is preferably 0.8 wt~ or less, more preferably 0.7 wt~ or less, further more preferably 0.6 wt~ or less in the cyclic oligomer content of the polyester in view of taste property. If the oligomer content of the polyester is too large, the taste property may become poor. The method for keeping the oligomer content of the polyester film in this range is not especially limited.
The oligomer content can be kept in this range, for example, by adopting any of the same methods as used for decreasing the acetaldehyde content of the polyester film.
To produce the polyester of the present invention, any conventional method can be adopted without any limitation.
For example, when polyethylene terephthalate is produced using germanium dioxide as the germanium compound, the following production method can be adopted. Terephthalic component and ethylene glycol are subjected to ester interchange reaction or esterification reaction, and germanium dioxide is added. In succession, polycondensation reaction is effected at a high temperature under reduced pressure till a certain diethylene glycol content is reached, to obtain a germanium-containing polymer. In this case, direct polymerization in which any ester interchange catalyst such as a magnesium-containing . ;~ 2186935 compound or manganese-containing compound is not substantially used is preferable, since the taste property of the film can be good. The obtained polymer is then polymerized in a solid phase at a temperature lower than the melting point of the polymer under reduced pressure or in an inactive gas atmosphere, to decrease the acetaldehyde content, for obtaining a predetermined intrinsic viscosity and a predetermined amount of carboxyl terminal groups.
In the present invention, in view of heat resistance and taste property, it is necessary to biaxially stretch a polyester containing ethylene terephthalate as a main component. The biaxial stretching can be either simultaneous biaxial stretching or sequential biaxial stretching. The inventors studied intensively the stretching conditions of the biaxially oriented film, and as a result, found that a biaxially oriented polyester film in which the breaking elongation in the machine direction (S MD) and the breaking elongation in the transverse direction (S TD) satisfy [Formula 1] and [Formula 2] is good in formability and impact resistance, that a biaxially oriented polyester film to be farmed into containers which contains 93 mold or more of ethylene terephthalate as a component and is 0.01 to less than 0.13 in face orientation coefficient is good in lamination property and formability, and that a biaxially oriented polyester film to be formed into containers which contains 95 mold or more of ethylene terephthalate as a component and is 120 to 220 kg/mm2 in amorphous Young's modulus is good in high speed formability. Thus, the present invention has been completed.
[Formula 1]
140 s (S MD + S TD)/2 s 300 S MD: Breaking elongation in the machine direction S TD: Breaking elongation in the tranverse direction [Formula 2]
~S MD - S TD~ s 60~
In the above formulae, the breaking elongation (~) is measured by pulling a sample of 10 mm in width and 50 mm in length at a tensile speed of 300 mm/min in 25°C 65~ humidity atmosphere using a Tensilon tensile tester.
The amorphous Young's modulus refers to the value calculated from the following formula, being the average of the values measured in the machine direction and in the tranverse direction.
Ea = (1 - ~)Ef Ea . Amorphous Young's modulus Crystallinity Ef . Young's modulus of film (p - 1.335)/0.12 p . Density measured by density gradient tube Furthermore, in view of formability and impact resistance, the average ((S MD + S TD)/2) of the breaking elongation in the machine direction (SMD) and the breaking elongation in the transverse direction (S TD) is preferably 160 to 300, more preferably 180 to 280.
In view of better formability at the upper part of the can, the difference in absolute value between the breaking elongation in the machine direction (S MD) and the breaking elongation in the transverse direction (S TD) is preferably 0~
to 50~, more preferably O~s to 40~. This range of difference can be achieved by properly controlling the temperature, speed and ratio of longitudinal stretching and the temperature, speed and ratio of lateral stretching when the film is formed, or furthermore the preheating conditions before respective stretching, and annealing conditions.
Moreover, in a tensile test at 75°C, the stress at an elongation of 100 is preferably l2 kg/mm2 or less, more preferably 11 kg/mm2 or less in the machine direction or transverse direction, in view of better formability. This range of stress can be achieved by properly controlling the temperature, speed and ratio of stretching when the film-is formed.
In the present invention, for better lamination property and formability, the face orientation coefficient is preferably in 218b93~
the above mentioned range, and especially in view of lamination property, the face orientation coefficient is preferably 0.02 to 0.125, more preferably 0.02 to 0.12. This range of face orientation coefficient can be achieved by properly controlling the temperature, speed and ratio of longitudinal stretching and the temperature, speed and ratio of lateral stretching when the film is formed, or furthermore the preheating conditions before respective stretching, and annealing conditions. The density in this case is preferably 1.385 g/cm3 to 1.42 g/cm3, more preferably 1.39 g/cm3 to 1.42 g/cm in view of formability.
The face orientation coefficient in this specification means fn = (Nx + Ny)/2 - Nz, where Nx, Ny and Nz are refractive indexes in the machine direction, tranverse direction and thickness direction respectively.
In the present invention, in view of better high speed formability, the amorphous Young's modulus is preferable in the above mentioned range, more preferably 120 to 200 kg/mm2, further more preferably 120 to 180 kg/mm2. This range of amorphous Young's modulus can be achieved by properly controlling the temperature, speed and ratio of longitudinal stretching and the temperature, speed and ratio of lateral stretching when the film is formed, or furthermore the preheating conditions before respective stretching; and ,. ~ ~ 218b935 annealing conditions.Prefarably it can be achieved by annealing in the high temperature or stretching in low ratio.
Furthermore, in the present invention, the relaxation time T1p of 1,4 benzene ring carbon atoms in the structural analysis by solid NMR is preferably 150 msec or more, more preferably 180 msec or more, further more preferably 200 msec to 600 msec in view of better lamination property and impact resistance. If the relaxation time Tlp is not in this range, not only lamination property but also impact resistance, particularly the storage stability of impact resistance may be lowered.
The relaxation time T1p expresses molecular mobility, and a higher T1p value means lower motility. This means that the T1p of benzene ring carbon atoms at 1,4 positions is preferably 150 msec or more in the state of biaxially oriented film, and this controls the molecular Constraint in this region, to inhibit the orientation at the time of lamination and to manifest excellent impact resistance. A relaxation time T1p of 150 msec or more can be achieved by applying any method to enforce molecular constraint when the film is formed, for later biaxial stretching.
Furthermore, the relaxation time T1p of carbonyl carbon atom in the structural analysis by solid high resolution NMR is preferably 250 msec or more, more preferably 300 msec to 900 msec in view of further higher impact resistance. The .- ~ 218693 relaxation time in this range can be achieved by applying any method to enforce molecular constraint when the film is formed, for later biaxial stretching.
In the present invention, the grain size of the (100) face obtained by X-ray diffractometry is preferably 6 nm or less, more preferably 5.5 nm to 2 nm, further more preferably 2.5nm to 5 nm or less, particularly preferably 4.5 to 3 nm in view of the control of crystal melting at the time of lamination.
Moreover, in the present invention, the formation as a laminated film is preferable, and it is desirable that the film consists of at least two or more layers, and that the difference in intrinsic viscosity between "the layer (I) on the side opposite to the side destined to contact the content of the container" and "the layer (II) in contact with said layer" is 0.01 to 0.5, in view of especially better formability and impact resistance. Especially when impact resistance is highly respected, the layer (I) to be laminated on the metallic sheet is desirably higher in intrinsic viscosity.
Furthermore, in the present invention, the thermal crystallization parameter oTcg of the polyester with ethylene terephthalate as a main component preferably satisfies [Formula 3], more preferably 70°C to 130°C, further more preferably 80°C to 130°C, in view of the crystallization ,~ 2186935 control after completion of annealing during can production, higher impact resistance, and higher formability in forming the laminated metallic sheet after completion of annealing.
The thermal crystallization parameter in this range can be achieved by controlling the catalyst, molecular weight, and by-production and addition of diethylene glycol.
[Formula 3]
60 (°C) s oTcg s 150 (°C) oTcg = Tc - Tg Tc: Heated crystallization peak temperature in DSC (°C) Tg: Glass transition temperature in DSC (°C) Furthermore, in the present invention, a film with a 0.01 to 3 ~cm thick adhesive layer laminated on the polyester film is preferable in view of especially high ratio formability, boiling heat resistance and good corrosion prevention. The adhesive layer can be made of any optional polymer which can be either a thermoplastic resin or thermosetting resin.
Preferably used polymers include epoxy resins, amide resins, acrylic resins, polyester resins, urethane resins, phenol resins, amino resins, their mixtures and copolymer resins, etc. In addition, a hardening catalyst, and a crosslinking agent such as a melamine compound or epoxy compound can also be mixed.
In the present invention, as described before, the film can be formed into containers, but in addition, the film can be laminated onto, for example, a paper sheet, plastic sheet, fibrous sheet, nonwoven fabric or metallic sheet, etc., to be formed into containers, since the film is excellent in formability, adhesive strength, impact resistance and taste property.
Especially it is preferable to laminate the film onto a metallic sheet for container production since a film as thin as 30 ~cm or less can be used and since the taste property, barrierability are excellent.
Furthermore, when a laminated metallic sheet with a metallic sheet as the substrate is formed by drawing or ironing, etc.
for subsequent production of metallic cans, the metallic cans can be used either as negative pressure cans or positive pressure cans since the substrate is made of a metal.
Especially when the substrate to have the film laminated is a metallic sheet selected from steel sheet, aluminum sheet and their surface treated sheets, it allows easy forming and is excellent in the impact resistance as cans preferably.
To most effectively form the film of the present invention into high performance containers, it is preferable to draw the laminated metallic sheet in one step or some steps. The metal can be preferably selected from, though not limited to, metals mainly composed of iron or aluminum, etc. in view of _. :~ 218b935 formability. Especially in the case of a metallic sheet based on iron, its surface can be covered with an inorganic oxide layer, for example, a chemical conversion layer applied by chromic acid treatment, phosphate treatment, chromic acid/phosphate treatment, electrolytic chromic acid treatment, chromate treatment, chromium chromate treatment, etc., to improve adhesive strength and corrosion resistance.
Especially it is preferable to coat with chromium oxide hydrate by 6.5 to 150 mg/m2 as chromium metal. Furthermore, a plating layer of a malleable metal such as nickel, tin, zinc, aluminum, gun metal or brass, etc. can also be provided. In the case of tin plating, the plating quantity is preferably 0.5 to 15 g/m2, and in the case of nickel or aluminum, the plating quantity is preferably 1.8 to 20 g/m2.
If the biaxially oriented polyester film of the present invention is 1 kg/15 mm or more in adhesive strength to the metallic sheet, it can withstand the forming by ironing or drawing, etc, and is especially good in impact resistance and storage stability of impact resistance preferably. The adhesive strength is more preferably 1.2 kg/15 mm to 6 kg/15 mm. The method for enhancing the adhesive strength is not especially limited. The adhesive strength can be enhanced, for example, by controlling the crystallinity of the polyester, increasing the molecular weight, intensifying the ~~ ~~~3'~
surface activation treatment, or providing an adhesive layer, etc., and any one or more of these methods can be optionally selected.
Moreover, in the present invention, if the adhesive strength to the metallic sheet after ironing or drawing, or after annealing subsequent to ironing or drawing is 250 g/15 mm or more, the formability at the upper part called the neck of the metallic can is improved, and the corrosion resistance after boiling treatment and the storage stability of corrosion resistance are improved preferably.
The adhesive strength is more preferably 400 g/15 or more, further more preferably 600 g/15 mm or more, especially preferably 800 g/15 mm or more. The method for enhancing the adhesive strength is not especially limited. The adhesive strength can be enhanced, for example, by controlling .the crystallinity, orientation and molecular motility of the polyester, increasing the molecular weight, intensifying the surface activation treatment, or providing an adhesive layer.
Any one or more of these methods can be optionally selected.
The thickness of the polyester film of the present invention is preferably 5 to 50 ~cm, more preferably 8 to 45 ~sm, further more preferably l0 to 40 ~cm, in view of the formability of the laminated metallic sheet, film formability on the metal, impact resistance and taste property.

The polyester film of the present invention is desirably 0.001 to 1 Vim, preferably 0.005 to 0.5 ~cm, more preferably 0.01 to 0.1 um in the average roughness Ra at least on one side of the film, in view of handling convenience, and high speed lamination capability. Furthermore, the ratio, Rt/Ra of maximum roughness Rt to average roughness Ra is preferably 3 to 40, more preferably 5 to 30, further more preferably 5 to 20, since defects such as pinholes are hard to occur in the film and since high speed lamination capability is good.
Moreover, to obtain the polyester film with the above surface properties, it is preferable that inorganic and/or organic grains of 0.01 to 10 ~m in average grain size are contained by 0.001 to 10 wt~. To prevent that the grains come off, it is preferable that inorganic grains and/or organic grains of 0.1 to 5 ~m in average grain size are contained by 0.005 to 3 wt~.
The inorganic grains and/or organic grains can be inorganic grains of, for example, wet or dry silica, colloidal silica, titanium oxide, calcium carbonate, calcium phosphate, barium sulfate, alumina, mica, kaolin, clay or aluminum silicate, and organic grains composed of styrene, divinylbenzene, silicone, acrylic acid, polyester, etc. Among them, inorganic grains of silica, calcium carbonate, aluminum silicate, etc. and organic grains composed of styrene, silicone, acrylic acid, methacrylic acid, polyester or divinylbenzene, etc. can be . ,~ 2186935 preferably used. Two or more kinds of these inorganic grains and/or organic grains can also be used together.
Using grains of more than 10 ~m in average grain size is unpreferable since defects are liable to occur in the film.
Especially when grains of 20 ~m or more are contained, the properties are greatly deteriorated. So, when the film is formed, it is preferable to use a filter which can greatly decrease foreign matters of 20 ~cm or more.
The average grain size of grains in this specification is obtained according to the following method. From the surface of the film, the polymer is removed by plasma low temperature incineration treatment, to expose the grains, and with the grains observed with a scanning electron microscope (SEM), the image of the grains is processed by an image analyzer. The observation is made at different places, and more than 5,000 grains are numerically processed. The number average diameter D obtained by it is identified as the average grain size.
D = ~Di /N
where Di is the circle equivalent diameter of each grain, and N is the number of grains.
Furthermore, to prevent the film from having defects caused by the coming-off of grains during forming, internal grains can be precipitated during polyester polymerization, to produce protrusions on the surface of the film.

~.
The method for precipitating internal grains is not especially limited. For example, a mixture containing an alkali metal compound or alkaline earth metal compound as an ester interchange catalyst can be polymerized according to a conventional, to precipitate grains in the reaction mixture.
As another method, during ester interchange reaction or polycondensation reaction, terephthalic acid, etc. can also be added. As a further other method, in esterification reaction, an alkali metal compound or alkaline earth metal compound can be arranged to exist before or after completion of esterification reaction, and polycondensation reaction can be effected in the presence of a.phosphorus compound, for precipitation. It is especially desirable in view of uniformity of grain size that the ratio (B + 0.5A)/P is 0.5 to 5, where A is the number of moles of the alkali metal compound, B is the number of moles of the alkaline earth metal compound and P is the number of moles of the phosphorus compound.
The amount of the internal grains is preferably 0.01 to 2 wt~, and can be obtained, for example, according to the following method.
Three hundred grams of o-chlorophenol is added to 30 g of a polyester sample, and while the mixture is stirred, the polymer is dissolved at 100°C in 1 hour. Then, an --ultracentrifuge Model 40P produced by Hitachi, Ltd. is mounted with a rotor RP30, and 30 cc of the solution is injected into each cell. The ultracentrifuge is gradually rotated to reach 30,000 rpm, and one hour later, the separation of grains is completed. Furthermore, the supernatant solution is removed, and the separated grains are taken. To the grains, o-chlorophenol of room temperature is added, for homogeneous suspension, and the suspension is ultracentrifuged, and this is repeated till the melt peak of the polymer by DSC does not appear any more. The separated grains thus obtained are dried in vacuum at 120°C for l6 hours, and weighed (in this case, if a catalyst, inorganic grains, organic grains, etc. are contained, the weights of the catalyst, inorganic grains, organic grains, etc. should be differently identified).
The internal grains can also be used together with other inorganic grains and/or organic grains.
In the case of a laminated film, the grains can be contained in any of the layers, but especially in view of impact resistance and handling convenience, it is preferable that the grains are added into a layer not laminated on the metallic sheet. The ratio D/d of the average grain size D (gym) to the thickness d (gym) of the layer is preferably 0.05 to 50, more preferably 0.1 to 10, and in view of better slipperiness, the ratio is preferably 0.5 to 5.

When a layer not containing grains is formed for better impact resistance, it is preferable that the layer laminated on the metallic sheet does not substantially contain any grains.
In the present invention, it is preferable the wet tension at least on one side of the film is 45 dyne/cm or more, more preferably 48 dyne/cm or more, further more preferably 50 dyne/cm or more in view of better formability and impact resistance.
The wet tension at least on one side of the film can be raised to 45 dyne/cm or more, for example, by any conventional method such as corona treatment, chemical treatment, flame treatment or plasma treatment, etc. Among them, corona treatment of surface is preferable as a method for enhancing impact resistance. As for the corona treatment, when a region of a powerful electric field locally exists as in the case where a high voltage is applied to an electric wire, discharge localized in the region occurs, and this is called corona discharge. Exposing the film to the discharge for surface treatment is called corona treatment. The corona treatment can also be effected in air, nitrogen or carbonic acid gas, and for example, the corona treatment as proposed in Japanese Patent Laid-Open (Kokai) No. 1-20236, Japanese Patent Publication (Kokai) No. 57-30854, etc. can be preferably used.
The intensity in the corona treatment is expressed by E value.

The E value is obtained as W/(D~V), where W is the treatment intensity (W), D is the treatment width (m) and V is the film speed (m/min). The E value is preferably 10 to 60, more preferably 15 to 50 in view of higher wet tension and freedom from surface defects. If the treatment is effected at a temperature lower than the glass transition point of the polymer, the wet tension of the surface can be effectively increased. It is preferable to apply the surface treatment on the side to be laminated on the metallic sheet.
Moreover, in the present invention, to improve the impact resistance after application of a heat history of higher than 200°C to the film and the impact resistance after application of about 100°C water treatment (boiling treatment) to the film, an antioxidant is contained preferably by 0.005 to 1 wt~, more preferably 0.005 to 0.5 wt~.
The antioxidant used is not especially limited, and can be preferably selected from conventional antioxidants including hindered phenols, hydrazines, phosphites, etc. Among them, pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], 3,5-di-t-butyl-4-hydroxy-benzylphosphonate-diethyl ester, 1,3,5-trimethyl-2,4,6-tris(3, 5-di-t-butyl-4-hydroxybenzyl)benzene, tris(2,4-di-t-butylphenyl)phosphite, etc. can be preferably used.
In view of taste property, it is preferable that the layer in ~- 2 i 86935 contact with the content of the container does not contain any antioxidant and that the layer laminated on the metallic sheet only contains an antioxidant.
In the present invention, when the film is in contact with content of the container and another film is laminated on the other side of the metallic sheet, the latter film is preferably biaxially oriented polyester film of 0.3 to 1, more preferably 0.3 to 0.9, further more preferably 0.5 to 0.9 in optical density in view of printability. Furthermore, the glossiness is preferably 50~ or more, more preferably 60~ or more, further more preferably 70~ to 110, in view of excellent printability and wear resistance.
To obtain such a film, not only the above mentioned grains, particularly titanium oxide or calcium carbonate, but also known grains with high hiding power can be used. For letting the film contain the grains, any known dispersing agent or grain surface treating agent can also be used.
The film of the present invention is especially preferably a laminated film. A layer containing 2 to 10 wt~ of grains can be laminated on the side not laminated on the metallic sheet (A/B), or another layer similar to said layer can also be laminated on the side to be laminated on the metallic sheet, to form a laminate of A/B/A, etc. In this case, the layer B
is preferably larger in grain content.

The polyester film of the present invention can be formed by any conventional method. The process for producing the film of the present invention is described below, but the present invention is not limited thereto or thereby.
The polyester is dried as required, fed into a conventional melt extruder, extruded as a sheet from a slit die, and brought into contact with a casting drum with static electricity applied, etc., to be cooled and solidified, for obtaining a cast sheet. For stretching, either simultaneous biaxial stretching or sequential biaxial stretching can be used. The cast sheet is stretched in the machine direction and in the tranverse direction, and annealed, to obtain a film with an intended face orientation. Preferably, in view of film quality, it is preferable to use a tenter oven, and sequential biaxial stretching of longitudinal stretching followed by lateral stretching or simultaneous biaxial stretching of stretching longitudinally and laterally almost simultaneously is desirable. The stretching ratios in the respective directions are 1.5 to 4.O times, preferably l.8 to 4.0 times. Either of the stretching ratios in the machine direction and the transverse direction can be larger, and they can also be equal. The stretching speed is desirably 1,000~/min to 200,000~/min. The stretching temperature is any temperature higher than the glass transition temperature of ~" 2186935 the polyester and lower than the glass transition temperature + 80°C, usually preferably 80 to 150°C. After completion of biaxial stretching, the film is annealed, and the annealing can be effected by any conventional method in an oven or on a heated roll. The annealing temperature can be any temperature higher than 120°C and lower than the melting point, preferably 120 to 245°C. The annealing time is optional, but is preferably 1 to 60 seconds. The annealing can be effected with the film relaxed in the machine direction and/or in the transverse direction. Furthermore, re-stretching can be effected once or more in each direction, and can also be followed by annealing. When a laminated film is produced, the polymer can also be co-extruded in layers before the die, or can also be melt-extruded for lamination after casting and before or after stretching.
Furthermore, when the polyester film of the present invention is produced, as required, additives such as antioxidant, plasticizer, antistatic agent, weather resisting agent, terminal blocking agent, etc. can also be used properly.
The methods for measuring and evaluating properties in the present invention are described below.
(1) Diethylene glycol content of polyester Measured according to NMR (13C-NMR spectrum).
(2) Melting point of polyester The crystallized polyester chips or film was measured by a differential scanning calorimeter (Model DSC-2 produced by Parkin Elmer) at a heating rate of 10°C/min.
(3) Intrinsic viscosity of polyester The polymer was dissolved into o-chlorophenol, and the relative viscosity was measured at 25°C, to obtain the intrinsic viscosity.
In the case of laminated film, the intrinsic viscosity of each layer of the laminated film was measured by scraping off the layer from the surface of the film using a knife (the layer remaining after scraping off can also be washed by a solvent such as o-chlorophenol, and measured).
(4) Germanium content of polyester Determined from the calibration curve between the germanium content of the polyester composition and the peak intensity obtained by fluorescent X-ray measurement.
(5) Acetaldehyde content Two gram of the polyester film as a fine powder was taken and put into a pressure vessel together with ion exchange water, and extracted with water at 120°C for 60 minutes, to determine by highly sensitive gas chromatography.

(6) Amount of carboxyl terminal groups (equivalents/ton) A polyester was dissolved in o-cresol/chloroform (7/3 by weight) at 90 to 100°C for 20 minutes, and potentiometric titration was effected by an alkali, to obtain the amount.

(7) Oligomer content One hundred milligrams of the polyester film was dissolved into 1 ml of ortho-chlorophenol, and the cyclic trimer was measured by liquid chromatography (Model 8500 produced by Varian), as the oligomer content.

(8) Average grain size From the surface of the film, the plastic resin was removed by plasma low temperature incineration, to expose the grains.
The treatment conditions were selected to incinerate the thermoplastic resin, but not to damage the grains. The grains were observed by a scanning electron microscope (SEM), and the image of the grains was processed by an image analyzer. The observation was made at different places, and more than 5,000 grains were numerically processed, to obtain the number average grain size D as the average grain size.
D = ~Di /N
where Di is a circle equivalent diameter of each grain, and N
is the number of grains.
In the case of internal grains, the section of a film slice can also be observed by a transmission electron microscope.

(9) Amorphous Young's modulus and breaking elongation (~) of .
film A sample of 10 mm in width and 50 mm in length was pulled at a _.
tensile speed of 300 mm/min using a Tensilon tensile tester, to measure the Young's moduli and breaking elongations (~) in the machine and tranverse directions of the film at room temperature according to ASTM-3-882-81 (Method A).
The amorphous Young's modulus in this specification refers to the value calculated from the following formula, being the average of the values measured in the machine and transverse directions.
Ea = (1 - ~)Ef Ea: Amorphous Young's modulus ~: Crystallinity Ef: Young's modulus of film (p - 1.335)/0.12 p: Density The density was obtained according to the density gradient method in water-potassium iodide aqueous solutions.
A tensile test at 75°C was also effected, to obtain the stress at an elongation of 100.

(10) Face orientation coefficient and refractive indexes The refractive indexes (Nx, Ny and Nz) in the machine direction, transverse direction and thickness direction were measured, with sodium D ray (589 nm in wavelength) as the light source, using an Abbe's refractometer, and the face orientation coefficient was obtained from fn = (Nx + Ny)/2 -~~ a693~
Nz.

(11) Surface roughness of film (average roughness: Ra, maximum roughness: Rt) The surface roughness was measured using a surface roughness tester. Measuring conditions were as follows, and the average of twenty measured values was adopted. The surface roughness tester used was a high precision thin film level difference tester ET-10 produced by Kosaka Kenkyujo.
Tip diameter of probe: 0.5 ~m Probe load: 5 mg Measuring length: 1 mm Cutoff: 0.08 mm Probe speed: 4 ~m/sec.
The definitions of Rt and Ra are, for example, described in Jiro Nara, "Methods for measuring and evaluating surface roughnesses (in Japanese)" (General Engineering Center, 1983).

(12) Relaxation time T1p The solid NMR measuring instruments used were Spectrometer JNM-GX270, solid amplifier, MAS controller NM-GSH27MU and Probe NM-GSH27T VT W respectively produced by Nippon Denshi.
The T1p (longitudinal relaxation in rotational coordinates) of 13C nucleus was measured.
Measurement was effected at 24.5°C at 50~.RH in a static magnetic field of 6.34 T (teslas). The resonance frequencies of 1H and 13C are 270.2 MHz and 67.9 MHz respectively. To eliminate the influence of anisotropy of chemical shift, MAS
(magic angle rotation) method was adopted. The rotational frequency was 3.5 to 3.7 kHz. The pulse series conditions were 90° against 1H, 4 ~m sec in pulse width and 62.5 kHz in rocking field intensity. The contact time for cross polarization from 1H to 13C was 1.5 msec. The retention time Z was set at 0.001, 0.5, 0.7, 1, 3, 7, 10, 20, 30, 40 and 50 msec. After lapse of retention time Z, the free induction damping (FID) of magnetization vector of 13C was measured (high output decoupling was effected to eliminate the influence of dipole interaction by 1H during FID measurement;
and to improve the S/N ratio, calculation was effected 512 times). The pulse repetition time was in a range from 5 sec to 15 sec.
Tlp value can be usually expressed by Tlp = ~(Ai)exp(-t/Tlpi) (Ai: Rate of the component to Tlpi). The peak intensities observed for respective retention times were plotted on semilogarithmic graph paper, and the Tlp value was obtained from the gradient. In this specification, analysis was made in a two-component system (Tlpl: amorphous component, Tlp2:
crystalline component), and the following formula was used to obtain the value by least square fitting.

..
Tlp = fa1~exp(-t/Tlp1) + fa2~exp(-t/Tlp2) fal: Rate of the component to Tlp1 fat: Rate of the component to Tlp2 fal + fat = 1 (13) Grain size x The grain size x of the (100) face was obtained by reflection X-ray diffraction using Scherrer's formula. The measuring X-ray wavelength was 0.15418 nm, and the diffraction of the (100) face was observed at a Bragg angle of about 12.7°.

(14) Thermal crystallization parameter of polyester The polyester was dried, molten, and quickly cooled, and the thermal crystallization parameter was measured by a differential scanning calorimeter (Model SC-2 produced by Parkin Elmer) at a heating rate of 16°C/min.

(15) Antioxidant content The film was dissolved into hexafluoroisopropanol, and acetonitrile was added to precipitate the polyester. The liquid was moderately concentrated and liquid chromatography was effected for determination.

(16) Wet tension of film surface Measured according to JIS K 6768. As the standard solution, the following three series were used; depending on the magnitude of surface tension.
30 dyne/cm s y < 56 dyne/cm: JIS K 6768 standard solution 2 i 86935 ._ 56 dyne/cm s y < 72 dyne/cm: ammonia water 72 dyne/cm s y: sodium hydroxide aqueous solution (17) Adhesive strength The adhesive strength of the film-laminated metallic sheet was obtained by a peeling test at an angle of 180° as an average of ten measured values. Also for the formed can, similar measurement was effected.

(18) Lamination property A tin-free steel sheet was heated to 280°C and laminated with the film. The laminated metallic sheet was quickly cooled, to measure the face orientation coefficient of the film laminated on the metallic sheet. This measurement was effected with ten samples, and the difference between the maximum and minimum values of the measured face orientation coefficient values was referred to for evaluation of lamination property according to the following criterion.
Grade A Less than 0.05 Grade B 0.005 to less than 0.01 Grade C 0.01 to less than 0.02 Grade D 0.02 or more (19) Formability a. Before annealing The film and a TFS sheet (0.25 mm thick) heated to 140250°C
were laminated at 50 m/min to have the layer B as the adhesive ~.. 2186935 side, quickly cooled, and formed by a drawing machine (drawing ratio (maximum thickness/minimum thickness) - 2.0, drawn in a drawable temperature range from 80 to 100°C), to obtain cans.
Into each can, 1 wt~ sodium chloride aqueous solution was poured, and allowed to stand for one day, and a voltage of 6 V
was applied between an electrode in the sodium chloride aqueous solution and the metallic can, to read the current value 3 seconds later. The average of ten cans was obtained.
Grade A Less than 0.001 mA
Grade B 0.001 mA to less than 0.01 mA
Grade C 0.01 mA to less than 0.05 mA
Grade D 0.05 mA or more b. After annealing The above laminated steel sheet was annealed at 200°C for 30 seconds, and drawn to 130 by a drawing machine, to obtain cans. Similarly, 1~ sodium chloride aqueous solution was poured into each can, and allowed to stand for one day. A
voltage of 6 V was applied between an electrode in the sodium ' chloride aqueous solution and the metallic can, to read current value 3 seconds later. The average of ten cans was obtained.
Grade A Less than 0.005 mA
Grade B 0.005 mA to less than 0.01 mA
Grade C 0.01 mA to less than 0.05 mA

Grade D 0.05 mA or more c. After boiling The cans of the above b were worked at the necks, filled with water, sealed and annealed at 100°C for 40 minutes.
They were opened, and 1 wt~ sodium chloride aqueous solution was poured into each can, and allowed to stand for one day. A
voltage of 6 V was applied between an electrode in the sodium chloride aqueous solution and the metallic can, to read the current value 3 seconds later. The average of ten cans was obtained.
Grade A Less than 0.005 mA
Grade B 0.005 mA to less than 0.01 mA
Grade C 0.01 mA to less than 0.05 mA
Grade D 0.05 mA or more (20) Impact resistance a. Can bottom Formed cans were annealed at 200°C for 30 seconds, filled with 350 g of water, covered, allowed to stand at 30°C for 72 hours, and dropped from a height of 30 cm onto concrete ground, so that the bottom face of each can might form an angle of 45°
against the ground. The water was removed, and the cans were masked with wax on the inside surfaces. Then, 1 wt~ sodium chloride aqueous solution was poured into each can, and allowed to stand for one day. A voltage of 6 V was applied _-between an electrode in the sodium chloride aqueous solution and the metallic can, to read the current value 3 seconds later. The average of teri cans was obtained.
Grade A Less than 0.3 mA
Grade B 0.3 mA to less than 0.5 mA
Grade.C 0.5 mA to less than 1.0 mA
Grade D 1.0 mA or more b. Storage stability of impact resistance The cans of the above a were allowed to stand for 7 days, to measure the impact resistance.

(21) Taste property (a) The polyester film was allowed to stand at 40°C for 14 days in contact with a flavor aqueous solution (30 ppm d-limonene aqueous solution) (500 cm2 in contact area), and heated at the glass transition temperature of the thermoplastic resin A + 5°C
for 30 minutes in nitrogen current, and the component expelled was analyzed by gas chromatography to determine the amount of d-limonene adsorbed per 1 g of the film for evaluation of taste property.
(b) The laminated steel sheet was pressurized at 100°C for 40 minutes in contact with water (1500 ml of distilled water for 2400 cm2). The extract was properly concentrated, and the total organic carbon (TOC) was measured by a TOC meter.
The present invention is described below in reference to 218b935 examples, but is not limited thereto or thereby.
Experimental example 1 An ethylene glycol slurry containing colloidal silica grains different in average grain size was annealed at 190°C for 2 hours. Then, the slurry was added to the esterified reaction mixture, and the mixture was polycondensed to produce chips of polyethylene terephthalate (PET) containing said grains by predetermined amounts (using germanium dioxide as a catalyst (Ge: 40 ppm) and phosphoric acid as a thermostabilizer, intrinsic viscosity 0.71, diethylene glycol 3 mold, oTcg =
82°C). This polyester was dried in vacuum at 170°C for 4 hours, fed into a single screw extruder, discharged from a die, and cooled and solidified by a cooling drum with mirror-finished surface, while static electricity was applied (7 kV), to obtain a cast film (drum rotating speed 30 m/min). The cast film was stretched to 2.9 times at 110°C in the machine direction (stretching speed 16300~/min), cooled to 40°C, preheated to 115°C for 3 seconds, stretched to 2.9 times at 118°C in the transverse direction (stretching speed 2000~/min), annealed at 190°C with 5~ relaxation for 5 seconds, and corona-treated in carbonic acid gas atmosphere. The film was 33 equivalents/ton in the amount of carboxyl terminal groups, 12 ppm in acetaldehyde content, and 0.45 wt~ in oligomer content.
The properties of the film obtained and the properties of cans are shown in Tables 1 and 8. It can be seen that the elongation, face orientation coefficient and amorphous Young's modulus were well controlled, and good formability, impact resistance and taste property could be obtained.
Experimental examples 2 to 15 Films shown in Tables 1 to 5 were produced as described for Experimental Example 1, except that the polyester production method, film forming method, lamination and the polyester used were changed. The results are shown in Table 8.
Experimental examples 2 to 9 used single-layer films, and were different in the polyester used and the film forming conditions. The physical properties of the films are shown in Table 1 to 3. In Experimental Example 2, the polyester contained 0.05 wt~ of (pentaerythrityl-tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]) as an antioxidant, and longitudinal stretching was effected at 108°C at a ratio of 3.2 times, while lateral stretching was effected at a ratio of 3.2 times. The annealing temperature was 225°C. As a result, even though the face orientation coefficient was high, the elongation and amorphous Young's modulus were controlled well. Though the lamination property slightly declained, other properities were good.
In Experimental Example 3, PET changed in crystallization rate by a catalyst was melt-extruded, cast, longitudinally 2) 8b935 w..
stretched at 108°C at a ratio of 2.9 times, preheated at 118°C
for 5 seconds, laterally stretched at 118°C at a ratio of 3.0 times, and annealed at 220°C. As a result, due to'poor elongation balance and low adhesive strength after forming, the formability and storage stability of impact resistance were low.
In Experimental Example 4, PET changed in crystallization rate by a catalyst and containing organic grains was melt-extruded, cast, longitudinally stretched at 108°C at a ratio of 3.0 times, preheated at 118°C for 5 seconds, laterally stretched at 2.8 times, and annealed at 220°C for 10 seconds. As a result, because of poor elongation balance and low adhesive strength after forming, the formability and impact resistance were low.
In Experimental Example 5, PET of Experimental Example 4 was longitudinally stretched at 111°C at a ratio of 3.3 times, preheated at 115°C for 3 seconds, laterally stretched at 3.3 times, and annealed at 170°C. As a result, due to large face orientation coefficient and low adhesive strength after forming, the lamination property, formability and impact resistance were low.
In Experimental Example 6, PET rather large in diethylene glycol content and high in molecular weight was longitudinally stretched at 107°C at a ratio of 3.5 times, preheated at 115°C
for 3 seconds, laterally stretched at 118°C at a ratio of 3.5 . - ~..
times, and annealed at 170°C. As a result, the face orientation coefficient and amorphous Young's modulus were large and the lamination property became especially poor.
In Experimental Example 7, longitudinal stretching at 108°C at a ratio of 3.0 times, preheating at 115°C for 5 seconds, lateral stretching at 2.9 times, and annealing at 180°C for 10 seconds were effected. As a result, because of poor elongation balance, high amorphous Young's modulus, and low adhesive strength after elongation, the formability and impact resistance were low.
In Experimental Example 8, PET further higher in crystallization rate was longitudinally stretched at 108°C at a ratio of 3.1 times, preheated at 115°C for 5 seconds, laterally stretched at a ratio of 3.05 times, and annealed at 183°C for seconds. As a result, because of high crystallization rate of polymer, the impact resistance after annealing was lower than that achieved in Experimental Example 7.
In Experimental Example 9, longitudinal stretching at 108°C at a ratio of 3.4 times, preheating at 115°C for 5 seconds, lateral stretching at 118°C a ratio of 3.2 times, and annealing at 170°C were effected. As a result, because of poor elongation balance, high face orientation coefficient and low adhesive strength after forming, the lamination property, formability and impact resistance were low.

Experimental Examples 10 to 15 used composite films and were different in the polyester used, film forming conditions, laminate composition and lamination conditions. The physical properties of the films are shown in Table 4 and 5, and the results are shown in Table 8. All the films were higher in adhesive strength and better in properties.
In Experimental Example 10, PET of 1.0 in intrinsic viscosity was laminated, and longitudinal stretching at 108°C at a ratio of 3.0 times, preheating at 118°C for 3 seconds, lateral stretching at 3.0 times, and annealing at 190°C were effected to obtain a film.
In Experimental Example 11, longitudinal stretching at 108°C at a ratio of 2.9 times, preheating at 118°C for 3 seconds, lateral stretching at 118°C at 2.9 times, and annealing at 190°C were effected to obtain a film, and it was coated with an organic solvent prepared by mixing a polyamidedicarboxylic acid modified epoxy resin, phenolformaldehyde resin and hardening catalyst at a ratio by weight of 50 . 49 . 1, by a coater.
In Experimental Example 12, the film obtained in Experimental Example 11 was coated with an aqueous solution containing a mixture consisting of a polyester-urethane resin and methylolated melamine at a ratio by weight of 95 . 5 and 10 wt~ of isopropanol, after corona treatment subsequent to longitudinal stretching in film formation.
In Experimental Example 13, a laminated polyester containing 0.1 wt~ of an antioxidant was longitudinally stretched at 108°C
at a ratio of 2.9 times, preheated at 118°C for 3 seconds, laterally stretched at 118°C at 2.9 times, annealed at 185°C, and furthermore, corona-treated in a carbonic acid gas-air mixed atmosphere on the side to be laminated on the metallic sheet at 40 in E value.
In Experimental Example 14, a laminated polyester containing 0.1 wt~ of an antioxidant was longitudinally stretched at 108°C
at a ratio of 2.9 times, preheated at 118°C for 3 seconds, laterally stretched at 118°C at 2.85 times, annealed at 185°C, and furthermore, corona-treated in a carbonic acid gas-air mixed atmosphere on the side to be laminated on the metallic sheet at 40 in E value.
In Experimental Example 15, the film of Experimental Example 1 was used as the inner face of the can. As the outer face of the can, a three-layer laminated film (17 um thick) consisting of A . B . A = 1 . 15 . 1 (where layer A was the same as the film of Experimental Example 1 except that 10 wt~ of rutile type titanium oxide grains of 0.3 ~,cm in average grain size were used and that the diethylene glycol was increased to keep the melting point at 250°C, and layer B was the same as the film of Experimental Example 1 except that 30 wt~ of rutile type titanium oxide grains of 0.3 ~cm in average grain size were used). The optical density was 0.78 and the glossiness was 85~, to provide good whiteness, and in addition, the amount of dust scraped during forming decreased remarkably.
Experimental examples 16 to 21 The physical properties of the films are shown in tables 6 and 7, and the results are shown in Table 8.
Experimental example 16 The film shown in Table 6 was obtained a-s described for Experiment Example 4, except that polyethylene terephthalate copolymerized with 15 mold of isophthalic acid was used as the polyester, that the longitudinal preheating and stretching temperatures were 95°C, that the longitudinal stretching ratio was 3.2 times, that the lateral preheating and stretching temperatures were 115°C, that the lateral stretching ratio was 3.3 times, and that the annealing temperature was 160°C. The results are shown in Table 8. Since the copolymerized amount was too large, the taste property and impact resistance were very poor.
Experimental example 17 The film shown in Table 6 was obtained as described for Experimental Example 16, except that the polyester used and the film forming conditions were changed (longitudinal preheating and stretching temperatures were 95°C; longitudinal stretching ratio was,3.3 times; lateral preheating and stretching temperatures were 115°C; lateral stretching ratio was 3.1 times; annealing temperature was 165°C). The results are shown in Table 8. Since the copolymerized amount was large and since the elongation balance was poor, the formability, impact resistance and taste property were poor.
Experimental examples 18 and 19 Films were obtained as described for Experimental Example 16, except that polyethylene terephthalate was annealed at 235°C
for 15 seconds and that the stretching ratio was 3.1 or 3.4 times. Since any of the elongation, face orientation coefficient and amorphous Young's modulus did not conform to the present invention, all the properties were poor.
Experiment example 20 A film was obtained almost as described for Experimental Example 16, except that polyethylene terephthalate copolymerized with 7 mole of isophthalic acid was used. Since the copolymerized amount was large and since the face orientation coefficient and amorphous Young's modulus were large, the lamination property, formability, impact resistance and taste property were poor.
Experimental example 21 A film was obtained as described for Experimental Example 16 21a6935 .-except that polyethylene terephthalate copolymerized with 10 mold of sebacic acid was used as the polyester, that the stretching temperature was 70°C and that the annealing temperature was 175°C. Since the copolymerized amount was large and since the face orientation coefficient was large, the lamination property, formability, impact resistance and taste property were poor.

Table 1 Experimental ExperimentalExperimental example 1 example 2 example 3 Polyester PET PET PET

p Ethylene terephthalate o component (mold) y Tm (C) 254 254 256 s nTcg (C) 82 82 68 t DEG (mol$) 3 3 2 a r Intrinsic viscosity 0.71 0.71 0.63 Material of grains Silica, Silica, Silica Silica Silica Average grain size 0.2, 0.8 0.2, 0.8 0.5 (gym) Content (wt~) 0.3, 0.05 0.3, 0.05 0.2 Thickness (um) 25 25 22 (SMD+STD)/2 (~) 212 182 170 P

r ~SMD-STD~ (~) 30 20 65 p Density (g/cm') 1.387 1.399 1.395 a Face orientation 0.118 0.134 0.123 coefficient (-) t Amorphous Young's modulus ( kg/mm ) s Intrinsic viscosity 0.68 0.68 0.61 f Relaxation time 134(ppm)211 220 205 f 164(ppm) 348 386 355 i 1 Grain size (nm) 3.6 5.3 4.5 m Surface roughness Ra(Ecm)0.012 0.016 0.010 Rt(~m) 0.165 0.240 0.162 Wet tension (dyne/cm) 48 41 42 Adhesive strength Sheet (g/15mm) Arter forming (g/l5mm)420 380 230 Table 2 Experimental exampleExperimental Experimental 4 example 5 example 6 Polyester PET PET PET

P Ethylene terephthalate 98 98 96 component (mold) Y

a Tm (C) 256 256 250 s t a nTcg (C) 65 65 82 r DEG (mold) 2 2 4 Intrinsic 0.63 0.63 0.8 viscosity Material of grainsCrosslinked Crosslinked Crosslinked polystyrene polystyrene polystyrene Average grain 0 0 0 size 3 3 3 (gym) . . .

Content (wt~) 0.2 0.2 0.2 Thickness (~cm) 25 25 25 P (SMD+STD)/2 (~) 169 176 150 o ~SMD-STD (~) 63 20 25 P

a Density (g/cm') 1.398 1.383 1.383 r t Face orientation 1 coefficient (-) 0.129 0.132 0.145 a s Amo hous Youn ~ 185 215 258 's d ~

o mo us (kg/mm ) f f Intrinsic 0.61 0.61 0.76 viscosity i 1 Relaxation time m 198 180 185 134(ppm) 164(ppm) 353 305 298 Grain size (nm) 5.2 2.9 2.9 Surface roughness0 0 0 Ra (Ecm) . . .

Rt (fcm) 0.275 0. 320 0. 260 Wet tension 42 42 42 (dyne/cm) Adhesive strength Sheet(g/l5mm) Arter forming 200 220 330 (g/l5mm) Table 3 ExperimentalExperimental Experimental example 7 example 8 example 9 Polyester PET PET PET

p Ethylene terephthalate 9g 98.5 98 o component (mold) y Tm (C) 256 256 256 a nTcg (C) 65 59 65 s t DEG (mold) 2 1 2 a .

r Intrinsic viscosity 0.68 0.67 0.68 Material of grains Calcium Calcium Calcium carbonate carbonate carbonate Average grain size (~cm)0.8 0.8 0.8 Content (wt$) 0.2 0.2 0.2 Thickness (~cm) 25 25 20 (SMD+STD)/2 ($) 165 169 172 P

r ~SMD-STD ($) 62 61 63 o Density (g/cm') 1.386 1.388 1.383 P

a Face orientation r coefficient (-) 0.126 0.129 0.132 t 1 Amorphous Young's modulus a (kg/mmz) 218 222 218 s Intrinsic viscosity 0.65 0.64 0.65 f Relaxation time 134(ppm)202 188 189 f 164(ppm) 347 310 309 i 1 Grain size (nm) 3.9 4.1 2.9 m Surface roughness Ra(Ecm)0.025 0.023 0.025 Rt(um) 0.335 0.331 0.375 Wet tension (dyne/cm) 42 42 42 Adhesive strength Sheet (g/15mm) Arter forming (g/l5mm) 240 200 230 2i 86935 Experimental Experimental Experimental example 10 example 11 example 12 Polyester PET PET PET

p Ethylene terephthalate o component (mold) ~

y Tm (C) 256 254 254 a nTcg (C) 70 82 82 s t DEG (mol$) 2 3 3 a r Intrinsic viscosity 0.71 0.71 0.71 Material of grains Silica, Silica, Silica, Silica Silica Silica Average grain size 0.2, 0.8 0.2, 0.8 0.2, 0.8 (gym) Content (wt~) 0.3, 0.05 0.3, 0.05 0.3, 0.05 L Polymer and features PET PolyamidedicaPolyester-a Intrinsic rboxylic acidurethane m viscosity modified resin +
1.0 i (Ge:30 ppm) epoxy resin Melamine +

n DEG:4.5 mold Phenolformaldcompound a Thickness: ehyde resin Thickness:
l0 +

t Ecm Hardening 0.1 um a catalyst d Thickness:

hem p Y

m a r Total thickness (~cm) 25 25 25 (SMD+STD)/2 (~) 175 212 212 P

r ~SMD-STD~ ($) 20 30 30 p Density (g/cm3) 1.387 1.391 1.391 a Face orientation r coefficient (-) 0.125 0.118 0.118 t 1 Amorphous Young's modulus a (kg/mm ) s Intrinsic viscosity 0.77 0.68 0.68 f Relaxation time 134(ppm)220 211 211 f 164(ppm) 358 348 348 i 1 Grain size (nm) 4.0 4.1 4.1 m Surface roughness Ra(Ecm)0.013 0.012 0.012 Rt(,um) 0.170 0.165 0.165 Wet tension (dyne/cm) 43 -(42) -(42) Adhesive strength Sheet(g/l5mm) Arter forming (g/l5mm)530 400 350 Table 4 ExperimentalExperimental example 13 example 14 Polyester PET PET

p Ethylene terephthalate o component (mold) 98 97 y Tm (C) 256 254 a nTcg (C) 70 82 s t DEG (mol$) 2 3 a r Intrinsic viscosity 0.71 0.68 Material of grains Silica, Silica, Silica Silica Average grain size (Ecm)0.2, 0.8 0.2, 0.8 Content (wt~) 0.3, 0.05 0.3, 0.05 L Polymer and features PET PET

a Intrinsic Intrinsic m viscosity viscosity 1.0 0.8 i (Ge: 30 ppm)(Ge: 30 ppm) n DEG: 4.5 DEG: 3.5 mol$
mold a Thickness: Thickness:

t ~cm um a d Antioxidant Antioxidant P

Y

m a r Total thickness (gym) 25 25 (SMD+STD)/2 (~) 185 198 P

r ~SMD'STD) ($) 10 15 o Density (g/cm') 1.387 1.388 P

a Face orientation r coefficient (-) 0.121 0.118 t 1 Amorphous Young's modulus a (kg/mm ) s Intrinsic viscosity 0.72 0.68 f Relaxation time 134(ppm)217 221 164(ppm) 359 349 i 1 Grain size (nm) 3.8 3.6 m Surface roughness Ra(Ecm)0.012 0.012 Rt(um) 0.190 0.169 Wet tension (dyne/cm) 53 54 Adhesive strength Sheet(g/l5mm) Arter forming (g/l5mm) 820 680 Table 5 218b935 Table 6 ExperimentalExperimental Experimental example 16 example 17 example 18 Polyester PET/1 PET/1 PET

p Ethylene terephthalate 83.5 83.5 98 o component (mold) y ~ (C) 222 222 256 s oTcg (C) 115 115 58 t DEG (mold) 1.5 1 2 a .

r Intrinsic viscosity 0.65 0.65 0.63 Material of grains Silica Silica Silica Average grain size (pcm)0.8 0.8 0.5 Content (wt~) 0.1 0.1 0.2 Thickness (um) 25 25 20 (SMD+STD)/2 ($) 195 215 138 p r ~SMD-STD ($) 50 65 35 p a Density (g/cm3) 1.370 1:375 1.409 r t Face orientation ' 0.128 0.125 0.155 i coefficient (-) a s Amorphous Young's modulus (kg/mm ) f Intrinsic viscosity 0.62 0.62 0.61 f Grain size (nm) 2.5 2.6 6.3 i 1 Surface roughness Ra(~m)0.022 0.022 0.012 m Rt (,ccm) 0 . 375 0 . 340 0.190 Table 7 ExperimentalExperimental Experimental example 19 example 20 example 21 Polyester PET PET/1 PETS

p Ethylene terephthalate 98 81.5 88 o component (mold) y '~ (C) 256 239 230-e nTcg (C) 58 95 ' 90 s t DEG (mol$) 2 1 2 a .

r Intrinsic viscosity 0.63 0.65 0.66 Material of grains Silica Silica Silica Average grain size (um)0.8 0.8 0.5 Content (wt~) 0.1 0.1 ~ 0.2 Thickness (gym) 20 25 20 (SMD+STD) /2 ($) 148 180 168 P

r ~SMD-STD (~) 65 30 45 P

a Density (g/cm') 1.409 1.373 1.384 r t Face orientation 0.145 0.135 0.145 i coefficient (-) a s Amorphous Young's modulus ( kg/mm ) f Intrinsic viscosity 0.61 0.62 0.63 f Grain size (nm) 6.1 2.7 3.8 i 1 Surface roughness Ra(um)012 0 0 m . . .

Rt(~m) 0.190 0.352 0.198 Table 8 Formability Impact Taste Lamination resistance pro ert p y ro ert p p y a b c a b a (~cg)b (ppm) Experimental example 1 .

Experimental B p, A B A A 14 1 example 2 .

Experimental A B B B A B 16 1 example 3 .

Experimental A B B B B B 16 1 example 4 .

Experimental B B B B B B 16 1 example 5 .

Experimental B B B B B A 12 1 example 6 .

Experimental A B B B B B 14 4 example 7 .

Experimental B B B B B B 14 1 example 8 .

Experimental B B B B B g 14 1 example 9 .

Experimental example 10 .

Experimental example 11 .

Experimental A A A A A A 13 1 example 12 .

Experimental A A A A A A 11 1 example 13 .

Experimental A A A A A A 13 1 example 14 .

Experimental A A A B A A 14 2 example 15 .

Experimental example 16 .

Experimental example 17 .

Experimental example 18 .

Experimental D C D D B C 17 2 example 19 .

Experimental C B C C C D 33 1 example 20 , .

Experimental D C C D C D 85 7 example 21 .

- 218~93~
Industrial applicability.
The biaxially oriented polyester film to be formed into containers of the present invention is excellent in the formability when formed into containers,.and also excellent in taste property, especially in the taste property after boiling, being able to be suitably used for metallic cans produced by forming.

Claims

1. ~A biaxially oriented polyester film to be formed into containers, comprising a polyester containing 93 to 100 mol% of ethylene terephthalate as a component, and having a breaking elongation (%) in a machine direction (S MD) and a breaking elongation (%) in a transverse direction (S TD) satisfying the following [Formula 1] and [Formula 2]:
[Formula 1] 140% <= (S MD + S TD) /2 <= 300%, [Formula 2] ¦S MD - S TD¦ <= 60%, and an amorphous Young's modulus of 120 to 220 kg/mm2.

2. ~The biaxially oriented polyester film according to claim 1, which has a face orientation coefficient of 0.01 to less than 0.13.

3. ~The biaxially oriented polyester film according to claim 1 or 2, wherein the S MD and S TD values satisfy:
¦S MD - S TD¦ <= 40%.

4. ~The biaxially oriented polyester film according to any one of claims 1 to 3, wherein a relaxation time T1.rho. of 1,4 benzene ring carbon atoms in a structural analysis by solid high resolution NMR is 150 msec or more.

5. ~The biaxially oriented polyester film according to any one of claims 1 to 3, wherein a relaxation time T1o of carbonyl carbon atoms in a structural analysis by solid high resolution NMR is 250 msec or more.

6. ~The biaxially oriented polyester film according to any one of claims 1 to 5, wherein a grain size of a (100) face obtained by X-ray diffractometry is 6 nm or less.

.DELTA.

7. ~The biaxially oriented polyester film according to any one of claims 1 to 6, wherein the polyester film consists of two or more layers, and a difference in intrinsic viscosity between a layer (I) on a side opposite to a side destined to be in contact with a content of the container and a layer (II) in contact with the layer (I) is 0.01 to 0.5.

8. ~The biaxially oriented polyester film according to claim 7, wherein the layer (II) contains 2 to 10 wt% of inorganic or organic grains.

9. ~The biaxially oriented polyester film according to any one of claims 1 to 8, wherein a thermal crystallization parameter .DELTA.Tcg of the polyester satisfies [Formula 3]:
[Formula 3] 60 (°C) <= .DELTA.Tcg <= 150 (°C) .DELTA.Tcg = Tc - Tg Tc: Heated crystallization peak temperature in DSC (°C) Tg: Glass transition temperature in DSC (°C).

10. ~The biaxially oriented polyester film according to any one of claims 1 to 9, wherein the polyester film and a 0.01 to 3 µm thick adhesive layer are laminated.

11. ~The biaxially oriented polyester film according to any one of claims 1 to 10, wherein the containers are made from a metallic sheet laminated with the film.

12. ~The biaxially oriented polyester film according to claim 11, wherein the laminated metallic sheet is drawn in one step or several steps.

13. ~The biaxially oriented polyester film according to claim 11 or 12, wherein an adhesive strength of the film to the metallic sheet is 1 kg/15 mm or more.

14. ~The biaxially oriented polyester film according to claim 13, wherein the adhesive strength of the film to the metallic sheet after completion of drawing is 250 g/15 mm or mare.

15. ~The biaxially oriented polyester film according to any one of claims 1 and 3 to 14, wherein an optical density is 0.3 to 1Ø

16. ~The biaxially oriented polyester film according to claim 15, wherein a glossiness at least on one side is 50% or more.

17. ~A process for producing a container, which comprises:~
laminating the biaxially oriented polyester film as defined in any one of claims 1 to 16, onto a steel or aluminum sheet, and then drawing and ironing the steel or aluminum sheet onto which the biaxially oriented polyester film is laminated.

18. ~A biaxially oriented polyester film adapted to be formed into a metallic can by laminating the polyester film on a steel or aluminum sheet and then drawing and ironing the laminated sheet, wherein:
the biaxially oriented polyester film is made of a polyester containing 93-100 mol% of ethylene terephthalate units and 7-0 mol% of other units derived from at least one member of (i) an aromatic, aliphatic or alicyclic dicarboxylic acid, (ii) a hydroxycarboxylic acid and (iii) an aliphatic, alicyclic or aromatic glycol;
the polyester has an intrinsic viscosity of 0.5 to 1.5 as measured in a solution of o-chlorophenol at 25°C, an acetaldehyde content of no more than 30 ppm, a germanium content of 1 to 500 ppm and a cyclic oligomer content of no more than 0.8 wt%;
the biaxially oriented polyester. film has at least one of the following properties (a), (b) and (c):
(a) a breaking elongation (%) in a machine direction (S MD) and a breaking elongation (%) in a transverse direction (S TD) satisfying [Formula 1] and [Formula 2]:
[Formula 1] 1400 <= (S MD + S TD)/2 <= 300%
[Formula 2] ¦S MD-S TD¦ <= 60%;
(b) a face orientation coefficient of from 0.01 to less than 0.13; and (c) an amorphous Young's module of from 120 to 220 kg/mm2; and the biaxially oriented polyester film is 5 to 50 µm thick, has an average roughness Ra of from 0.005 to 0.5 µm and contains therein 0.005 to 3 wt% of inorganic or organic grains having an average grain size of 0.1 to 5 µm.